Wikipedia:Reference desk/Archives/Science/2007 April 20

= April 20 =

Help me create a simple circuit to power an inverter
I am planning to make a smallish breadboard-mounted mechanism which can be used to power a cold cathode florescent backlight. I think the best way to do this is to use an AC-DC "wall wart" to power a DC-AC inverter. In particular, I'm looking at this one: http://www.ergpower.com/pdf30/D8MD60J2.pdf (65KB PDF). This inverter has four inputs: Vin(+), Vin(-), Enable, and Control. Supposedly, it nominally takes a 12V input.

Question 1: Can I connect a normal 12V wall wart to Vin(+) and Vin(-)? (I am presuming "yes".)

Question 2: Is Vin(-) basically the same as "ground"? (I am presuming "yes".)

Question 3: Does the Control input vary the output voltage depending on the difference between the Control voltage and ground? (I am presuming "yes".)

Question 4: I think the best way to easily change the Control voltage is with a potentiometer hooked up to Vin(+), Vin(-)/ground, and Control. I guess I need to adjust this voltage between ~0V and ~6V. What kind of potentiometer would I need, and what would the specs need to be? It looks like potentiometers are often rated as "x ohms". Does this rating mean the potentiometer can adjust between 0 and x ohms?

Question 5: What the heck is the "Enable" input?

Thank you for any consideration. I am more than willing to provide clarification on any point.

--Mbliref 04:42, 20 April 2007 (UTC)


 * 1. Yes, provided that it can provide enough current.
 * 2. Yes, but don't connect that to the ground in your power socket, or you will trip the ground fault protection thing. Connect it to V-
 * 3. Yes, it's forming a voltage divider between them.
 * 4. Basically any linear pots would do, but get a high resistance one to minimise the wasted current through the pot, probably a 10k linear one as those are quite common.
 * 5. If Enable is pulled up to V+ level, it turns on, otherwise it turns off, works like a switch so you don't have to touch the V+/V- wires. --antilivedT 06:07, 20 April 2007 (UTC)


 * 1. Iffy. Some power supplies supply more than 12.0 volts when they're rated at 12 V. For example, I have one here that's 5V but supplies 7.5V. It's not because it's broken, it's because it's designed to be higher sometimes to work with voltage regulators onboard the unit. So the answer is yes, if you measure a ~12.0V and not a 14.0V+ out of the power supply.
 * 2. There are two different types of grounds. Earth ground and common ground. Earth ground is the third prong on a plug that directs all bad current to earth. Common ground is the lower potential, sometimes ground, sometimes a negative voltage, sometimes even a positive voltage. So like Antilived said, connect that to the lower potential, which is "negative" in this case.
 * 4. As Antilived said, choose at least a 10K pot. But yes, a 10K pot means you adjust between 0 and 10K. They're fairly common and cheap. --Wirbelwind ヴィルヴェルヴィント (talk) 06:38, 20 April 2007 (UTC)


 * 4 on the pot side of things, you only need to adjust the control voltage from 0 to 5 volts according to the data sheet, so half of your adjustment range will do nothing. So you can add another 10K resiseter in series with the POT on the +ve side, so that it adjusts between 0 and 6 volts instead, and you will get more useful control.  GB 07:41, 20 April 2007 (UTC)


 * For voltage adjustment, you might want a linear pot instead of an audio taper pot. Edison 23:15, 20 April 2007 (UTC)


 * Thanks, Everybody! I'm so glad that you have pretty much the same answers. That means you're probably correct. :-) I'll look into that extra resistor--might be a good plan. Thanks for the suggestion. Damn, Wikipedia (i.e., Antilived, Wirbelwind, GB, and Edison) is cool. --Mbliref 02:15, 21 April 2007 (UTC)

Provisions for nuclear warfare or WMD with extraterrestrials
What provisions exist on Earth to deal with an alien war, if it were to occur? I know it sounds merely sci-fi (Independence Day, Star Trek: First Contact), but I was wondering if Space Command or any other treaty of global alliance has been on the backburner in case it were to happen. Neustriano 05:41, 20 April 2007 (UTC)


 * Presumably we would be helpless against any civilization with the will to destroy us and the technology to reach us, so I think such plans would be worthless. anonymous6494 06:22, 20 April 2007 (UTC)


 * Duck and cover? And as a last resort...Slim Whitman! Clarityfiend 06:24, 20 April 2007 (UTC)


 * People tend to neglect the immense home-field advantage in hypothetical interplanetary war. We would be able to feed and supply a huge ground army; and mobilize a vast array of "short-range" air superiority tactics, which would not be possible for an invading fleet many millions of miles from its home base.  Nimur 07:07, 20 April 2007 (UTC)

The thing about this is that if any space-faring extraterrestrials wanted us dead, you wouldn't be around to ask the question of how we'd defend against them, now would you? If they can travel across the vast emptiness of space without a hitch, they're probably going to be light-years ahead of us in tactics, weaponry, psych-ops, you name it. Vranak


 * I don't think they want to invade they seem happy just to kidnap and probe rural Americans, for some unknown cultural reason137.138.46.155 07:51, 20 April 2007 (UTC)


 * Best tactic for hypothetical invading aliens would be to hide in the asteroid belt and push rocks in our direction. A few impact events would bring an end to civilisation as we know it and survivors would be too busy surviving to mount any effective defense. Earth would be like a city under siege - but with no walls. Not an original idea, of course - see Footfall. Gandalf61 09:55, 20 April 2007 (UTC)


 * We had this question quite recently - it's very clear to me that if such aliens could get here over interstellar distances, they would have the technology to stand off so far away (like maybe the asteroid belt) that we could never reach them. Then they could nudge mountain-sized rocks out of their orbits and take us out very easily. The problem for us is that the earth is a large target and it's trivial to know exactly where it will be at any time in the future so it's very easy to hit. If they aim large rocks at us, we are powerless to avoid them. On the other hand, if we put a large collection of nukes onto our best and fastest rocket it would take a couple of years to get to them - giving them plenty of time to move their agile spacecraft a few hundred miles out of the way and avoid it completely. But that assumes we'd even know they were there - our present technology would be unable to spot moderately large spacecraft at the distance of the moon - let alone out at the asteroid belt - let alone hiding on the far side of an asteroid. They could start those mountain-sized rocks heading towards us - and we wouldn't know there was anything happening until they were well on their way - we'd be wondering what caused this mysterious rain of city-smashers right up until the time they hit. Truly - any alien who could get here could crush us like bugs without us even knowing they existed. There is nothing whatever we could do against such a civilisation. Footfall was OK - but the aliens were stupid and did it from orbit rather than from the asteroid belt. We'd never have beaten them if they'd done that. SteveBaker 12:53, 20 April 2007 (UTC)


 * Perhaps we could obtain the secret plans for their Deathstar which would reveal an opening to a shaft leading into the reactor core, where a small nuke could cause the rapid vaporization of the craft. And then there was a cartoon in National Lampoon or some such journal during the Reagan administration which showed Ronald Reagan out in space whacking enemy missiles with a giant "particle-board beam." Something like that might work. But once they invaded they could never give up and leave, because we might follow them home. Edison 16:23, 20 April 2007 (UTC)

We have the | Near Earth Object Program which *might* let us see them coming. Then we would at least have a nice view of the pretty interstellar spaceships before aforementioned kinetic missiles whacked our civilization into submission. Eldereft 07:37, 21 April 2007 (UTC)


 * Yeah - but they can only detect rocks bigger than 140 meters and at distances less than 1.3 au. The asteroid belt is out at 2 to 3 au - and a 139 meter rock could do one heck of a lot of damage if aimed accurately. SteveBaker 16:38, 21 April 2007 (UTC)

Removed poor attempts at political humor.

magnetic flux
A solid conductor of circular cross section is made of a homogeneous non magnetic material.if radius is a = 1mm, the conductor lieng on the z axis, current flowing in the az direction find 1.the total magnetic flux ouside the conductor I used the amperes circuit law but got some numerical answer however the answer was infinity how can that be?? this is a drill problem from the sixth edition of Engineering electromagnetics by william Hyte and john A.Buck 6th edition.


 * possibly the conductor is infinite in length -as long as a z-axis is! GB 06:42, 20 April 2007 (UTC)

Dear Tiny Little Nuke
What is theoretically the smallest, in term of tons of TNT, a nuclear (or atomic) bomb can be? Has one that small ever been detonated?--JLdesAlpins 11:08, 20 April 2007 (UTC)


 * Depends on what you mean by a bomb, a single Uranium-235 atom getting hit by a neutron and fissioned without causing chain reaction is a nuclear device, albeit a very very weak one, almost negligible. --antilivedT 11:31, 20 April 2007 (UTC)


 * An amazing anecdote from The Making of the Atomic Bomb (page 259): the fission of a single uranium atom releases enough energy to make a grain of sand visibly jump (around 200 MeV)! --TotoBaggins 19:05, 20 April 2007 (UTC)


 * Well I still stand by my statement. A grain of jumping sand is the last of my worries if I was in a war :p. --antilivedT 09:30, 21 April 2007 (UTC)

To make a nuke-bomb handgrenade, you would have to get around the Critical mass problem. --Zeizmic 11:48, 20 April 2007 (UTC)


 * As low as 1kt is easyly possible. Search for a element with low critical mass 12-20kg I recal was a minimum of some exotic plutonium isotop, it is used in the backpack nukes already developed. Than mess up the explosives in the compression explosives and your bomb would only try to start exploding and end befor much damage is done (the gamma ray impulse will be good enough to kill the people watching. The builders of the first bob did something like that).--Stone 12:08, 20 April 2007 (UTC)


 * Depends how many free neutrons you have around. The "critical mass" varies depending on a lot of factors. And please be sure to see our Davy Crockett (nuclear device) article.


 * Atlant 12:41, 20 April 2007 (UTC)

I have see a film about the Davy Crockett (nuclear device) and in that time generals really thought to use this as a close range weapon in infantry battle.--Stone 12:59, 20 April 2007 (UTC)


 * Our article on Davy Crockett (nuclear device) suggests a yield of 10-20 tons of TNT (this link gives the yield of a test firing as 18 tons) and a lethal radius of less than 500 metres. Most feasible usage would have been as an area denial weapon, creating irradiated zones to slow the advance of infantry. Gandalf61 13:17, 20 April 2007 (UTC)


 * You can go even lower than that if you are happy with a mis-fire, a fizzle. But now you're probing the boundary between atomic bomb and dirty bomb. --24.147.86.187 21:37, 20 April 2007 (UTC)

eye colour changing
this is quite werid, im 15 and i've got rich brown eyes but for some reason over the past few months i've been noticing a change in colour and there quite golden/amberish brown now,i originally thought i was imagining it at first but my mom and my friends have started noticing the change in colour, so why is it happening and has anyone here had a similar experience??? :D


 * Change in eye colour can be a natural process or it can be caused by disease: . Seek the opinion of your physician or other medical professional; Wikipedia cannot offer you medical advice. TenOfAllTrades(talk) 14:55, 20 April 2007 (UTC)


 * It certainly has been known to occur without being associated with any particular morbidity (says the guy whose eyes were once...), but that doesn't say why your eyes are changing color.


 * Atlant 14:58, 20 April 2007 (UTC)


 * There are people whose irises change color with their mood. Vranak


 * Many people's irises are variegated and will show different colors based on the size of the pupil opening. That may track mood (it's common for pupils to dilate when someone is looking at something/someone they like) or it may just reflect the intensity of the ambient lighting.


 * Atlant 15:51, 20 April 2007 (UTC)


 * I had bright blue eyes when I was younger. Now they're a steely grey. It was a very gradual change, over many years. Get yours checked out, just to be on the safe side. --Kurt Shaped Box 17:40, 20 April 2007 (UTC)


 * The use of some drugs can result in a change in eye colour. Some treatments for glaucoma, such as prostaglandin analogs, are known to change eye colour in maybe 10% of patients. These combat glaucoma by increasing drainage of intraocular fluid, thereby lowering pressure. Its thought that prostaglandin acts on eye colour by mimicing a natural hormone that mediates melanin production. People have reported that, when they are ill or under stress, that their eye color becomes darker or lighter. A modified version of the pigmentary hormones are also produced during stress (and when you stress fish and frogs, they change colour for this very reason). Interestingly, marijuana has also been used as a drug to lower intraocular pressure in people with glaucoma and has a stress relieving effect. There are occasional reports that the use of marijuana can result in eye color change, but no scientific studies backing it up. Rockpock  e  t  18:48, 21 April 2007 (UTC)

I've said this a few times before and people often complain but c:), you can do things like this through will power, concentrating on what you want to happen, and it sometimes works, so you could try this if you want to get back to your original colour :) HS7 10:26, 22 April 2007 (UTC)

The same thing happened to me a few months ago. But I don't think anyone has noticed yet. Although I do spend a lot of time by myself and my family isn't usually very observent, so I shouldn't be suprised. You don't happen to have even lighter brown patches in your eyes too, do you?

my eyes are like light brown with golden/amber tones, but dark around the edge of the iris quite unusual but cool :D, also thanks to everyone with their knowledge and experiences :D

Difference between illness and syndrome
What's the difference? Thanks. --Taraborn 15:41, 20 April 2007 (UTC)


 * Syndrome defines itself as a set of "essential characteristics", signs or features that are associated with an illness, such as swearing and twitching in Tourette's syndrome, but to confuse the issue, it is often used in the names of illnesses as well. Clarityfiend 16:49, 20 April 2007 (UTC)


 * I would hazard to suggest that 'illness' has connotations of being life-threatening but treatable, while 'syndrome' suggests something you can live with, but isn't treatable. Vranak


 * Usually the distinction is between syndrome and disease, not syndrome and illness. "Illness" is a rather general that simply means "not healthy". --David Iberri (talk) 22:26, 20 April 2007 (UTC)

Feraliminal Lycanthropizer
Where can I find a reasonably neutral introduction to the device known as the Feraliminal Lycanthropizer and its claimed effects on human behaviour? Neon Merlin  16:46, 20 April 2007 (UTC)


 * A brief summary review of the little legitimate literature suggests that it's entirely bollocks. The Fortean Times offers a readable (and footnoted) survey of acoustic weapons and manipulation techniques in this article. TenOfAllTrades(talk) 17:01, 20 April 2007 (UTC) (minor correction by TenOfAllTrades(talk) 17:26, 20 April 2007 (UTC))

The efficiency of pro-vitamin A's
There are several carotenoids which can be converted to retinol by the human body, most noteably beta-carotene. My question is: How much retinol is typically made of a certain amount of ingested beta-carotene (when the body does not have surplus amounts of either retinoids or pro-vitamin A's)? The British Foods Standard Agency says that it's 1/6. The values in the USDA food database seem to imply a factor closer to 1/2 (note about the values in the database: 1 IU = 1 International Unit is equivalent to 0.3 &mu;g retinol). I know that it also depends on the bioavailability - the uptake from the intestine - of beta-carotene, which is raised by fatty food; so let's say that one eats enough fat for efficient uptake. What is the typical conversion factor for beta-carotene and other pro-vitamin A's like alpha-carotene and beta-cryptoxanthin? Icek 17:59, 20 April 2007 (UTC)

Heat-stability of choline
In the USDA food database the value for choline in raw eggs is 251.1 mg/100 g, but there is no value for hard-boiled eggs. Therefore my question: How is choline (bound in lecithin, as in the egg) or its bioavailability affected by heat treatment? Icek 18:06, 20 April 2007 (UTC)


 * It might have been a mistake to list any choline in raw eggs, as this site lists none: . StuRat 17:06, 21 April 2007 (UTC)


 * Only to clarify, "no value" usually only means that there is no data, not that there is only a negligible amount of the substance. Raw egg yolk does contain lecithin (Wikipedia's article actually says that the word "lecithin" comes from the Greek word for "egg yolk") and therefore choline, I'm quite sure of that. Icek 06:52, 22 April 2007 (UTC)

Peptobismol and antibiotic action
I'm a nerd so here goes:

why is peptobismol a mild antibiotic? it obviously has something to do with the bismuth since salicylate is an anti-inflammatory.

is bismuth bacteriostatic or what.


 * I have never heard of this effect, and the explanation doesn't appear in our article. Can you tell where you first heard this idea?  Nimur 20:27, 20 April 2007 (UTC)
 * It's on the article for the active ingredient. It does indeed appear to be due to the Bi; the footnotes of give several lead-refs and review-articles if you want them. DMacks 20:31, 20 April 2007 (UTC)

Many thanks, chief. cyanide_sunshine